As a method for detecting and tracking a position of a moving object (for example, a person) that freely moves around in a space, there are proposed methods implemented with an image processing utilizing a camera image and a detecting method utilizing a range sensor, such as a laser range sensor.
In a method for tracking the moving object using the range sensor, a shape of an object and a time continuity of a position and a velocity of the object are utilized. However, according to the conventional tracking method, it is difficult to specify what type of physical object the object belongs to. For this reason, reliability in tracking the object becomes deteriorated when used in an environment congested with a plurality of objects.
Therefore, there has been proposed a method using a continuity of a laser reflection intensity in grouping detected points measured by a laser range sensor. An example of such method is disclosed in JP-A-2004-198323.
On the other hand, by employing the method using an image processing, tracking while specifying a target object can be performed. However, it is difficult to accurately specify a position of the target object due to a matching accuracy, a misrecognition, and a resolution of a camera sensor.
In order to solve the problems, there is used a method called “sensor fusion”, in which a multiple sensors are employed for combining advantages of each of the sensors. However, there has not been established a robust tracking method for tracking a moving object that irregularly moves at a high speed in an environment where a plurality of objects exist.
There has been proposed a method using a sensor fusion unit that employs distance and azimuth information output from a radar to a determination result of an image processing of a captured image. An example of such method is disclosed in JP-A-2005-297648. There is also proposed a method that changes a weight for image information in accordance with a brightness level of a surrounding circumstance. An example of such method is disclosed in JP-A-2007-015676 (counterpart U.S. publication is: US 2006/0274149 A1).
In the document JP-A-2004-198323, in a case in which a measuring surface of the target object is not uniform, a tracking performance becomes deteriorated. Accordingly, the method may only be suitable for tracking an object having a predetermined shape and size, such as a vehicle. Moreover, the method is not suitable for tracking an object in a situation where other objects exist near the target object, as such in a so-called congested situation.
In measuring a distance using a stereo image processing, in addition to affection due to image processing, such as misdetection and matching error, a quantization error caused by a pixel density of a camera sensor will affects the measurement result. Depending on a type of a camera sensor to be used or a parallax of the camera sensor, accuracy in a stereo viewing measurement of an object placed at a distance of several meters reaches several tens of centimeters in some cases. In the method described in the document JP-A-2005-297648, although the misdetection can be checked, a resolution cannot be obtained beyond a camera image processing so that tracking for a high speed operation cannot be performed.
In the sensor fusion system based on a captured image as those disclosed in the document JP-A-2007-015676, there is a problem in that an operating performance cannot be basically expected beyond a camera image processing and an operation in a congested environment is also difficult to perform.